The operation of a railway requires the transmission of a large quantity of information, some of which is safety critical (so called “vital”) and some of which is not. Yet, most railway systems have only limited channel and data-rate capabilities. An example of the information flow through a conventional railway system is discussed below in more detail in conjunction with FIG. 1, which depicts a portion of prior-art railway system 100.
FIG. 1 depicts central control center 102, main line 104, branch lines 106, 108, and 110, track switches 112, 114, and 116, and trains 118, 120, and 122. The central control center, the trains, and the track switches all have telecommunications capability (e.g., a radio, etc.). Communication occurs over a single, multiple access communications channel.
Train 118 is assumed to be inactive on branch line 108. When train 118 is “awakened” (i.e., turned on from a cold start), it will receive a large quantity of initializing information (e.g., a guide-way data base, etc.) so that it can determine its location and integrity, among any other functions. This information is typically transmitted from central control 102, as well as railway features, such as switches 112, 114, and 116.
Before train 118 is permitted to move along a guide-way, it must receive authorization to do so from central control 102. Before the center will issue authorization, it must receive information about the location (i.e., block occupancy) of requesting train 118. It must also have information about the block occupancy of nearby railway track, such as main line 104 and branch lines 106 and 110. Trains 120 and 122 will report their position to central control 102. Furthermore, central control will require information concerning the state of nearby track switches, such as switches 112, 114, and 116. Control center 102 will therefore query those switches as to their state (or the switches might regularly broadcast their state).
Much of the information that is being transmitted to and from trains, central control, and railway features during normal operations is not vital (safety critical). Unfortunately, depending on the access protocol used, the transmission of such non-vital information might preclude the transmission and/or receipt of vital information. This introduces inefficiencies and delays into the system.
The simplest approach for addressing this problem is to installed advanced communications systems, which will provide increased bandwidth and telecommunications capabilities. But that is an expensive approach, and one that infrastructure owners have been reluctant to pursue.
An approach is therefore needed to provide vital communications information on high-demand networks.